Conventionally, there is known a bearing device for a vehicle wheel that rotatably supports a wheel in a suspension system of an automobile or the like, and includes a rotational speed detecting device that detects the rotational speed of the wheel. In the bearing device, a hub wheel to be connected to a wheel is rotatably supported via rolling elements. The rotational speed detecting device of the bearing device is configured of a magnetic encoder in which different magnetic poles are alternately magnetized in the circumferential direction, and a magnetic sensor. In the bearing device, the magnetic encoder is fixed to the hub wheel, and the magnetic sensor is disposed at a portion where it does not rotate along with the hub wheel. The bearing device can detect the rotational speed of the wheel connected to the hub wheel from intervals of changes in the magnetism when the magnetic encoder, rotating along with the hub wheel, passes near the magnetic sensor.
As a bearing device for a vehicle wheel of such a type, there is one in which a magnetic encoder is protected by a cover in order to prevent erroneous detection due to a damage by flying stones or the like, or adhesion of mud, magnetic material, and the like, to the magnetic encoder of the rotational speed detecting device. The magnetic encoder is hermetically sealed inside the outer ring in such a manner that the opening of the outer ring of the bearing device is covered with a nonmagnetic cover. With this configuration, the bearing device can detect a change in the magnetic properties of the magnetic encoder by the magnetic sensor while protecting the magnetic encoder from flying stones and mud. For example, Patent Literature 1 describes as provided below.
A rolling bearing unit with an encoder (bearing device for a vehicle wheel) described in Patent Literature 1 includes an outer ring (outer member), a hub body (inner member), a cover, and an encoder. Inside the outer ring, the hub body is rotatably supported via rolling elements. In the vicinity of the rolling elements, grease for lubrication between the rolling elements and the hub body and between the rolling elements and the outer ring is injected. To one side end of the hub body, an encoder is fixed via a support ring (support ring). A bottomed cylindrical cover is fitted to the opening of the outer ring facing the detection surface of the encoder. The rolling bearing unit with the encoder is attached to a knuckle of a wheel suspension system, and a magnetic sensor (not illustrated) that rotates the encoder is supported by the knuckle.
The cover is formed such that a cylindrical portion (side portion), an outer diameter side flat plate which is a disk-shaped bottom face, and an inner diameter side flat plate are integrated via a connecting plate. Thereby, the cover of the rolling bearing unit with the encoder encloses the grease and the encoder therein with the cover and prevents mud and foreign materials from entering the grease and the like, and also protects the encoder from mud, a magnetic material, and the like. However, in the rolling bearing unit with the encoder, a space for installing the encoder is formed on the outer side (inner side) from the rolling element. Therefore, there is a possibility that the grease sealed in the vicinity of the rolling element is scraped out by the rotation of the rolling element and flows out to the space where the encoder is provided. Therefore, in the rolling bearing unit with the encoder, it is necessary to enclose the grease in consideration of the amount of grease outflow into the space where the encoder is installed.